<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .box {
            position: relative;
            width: 536px;
            height: 294px;
            margin: 200px auto;
        }

        .box img {
            width: 100%;
            height: 100%;
        }

        .hd {
            position: absolute;
            top: 0;
            left: 0;
            display: none;
            width: 536px;
            height: 294px;
            background: rgba(0, 0, 0, .4) url(images/arr.png) no-repeat center;

        }

        /* 当我们鼠标经过box，就让遮罩层显示出来 */
        .box:hover .hd {
            /* 显示元素的意思 */
            display: block;
        }
    </style>

</head>

<body>
    <div class="box">
        <img src="images/tb.png" alt="">
        <div class="hd">
        </div>
    </div>

</body>

</html>